1. Field of the Invention
This invention relates generally to the field of blow molded plastic containers, and more specifically to a rectangular blow molded plastic container that has improved resistance to deformation such as saddling.
2. Description of the Related Technology
The extrusion blow molding process involves capturing a portion of a hot, continuously extruded parison of plastic material in a moving mold, which may be mounted on a shuttle or a rotating wheel. The captured plastic material is inflated against the interior of the mold, forming a hollow article. Flash material is typically trimmed from the article after it has been ejected from the mold.
Various consumer products, such as food products, are packaged for sale in extrusion blow molded plastic containers that are sealed with a closure. One type of such container is shown in FIG. 6. It includes a generally rectangular main body portion and a finish portion that has a circumferentially extending snap bead. The finish portion has an upper surface that defines a rim framing an opening that provides access to the interior of the container.
One problem that has persisted in the manufacture of containers of the type that are shown in FIG. 6 is that the central portions of the upper rim tend to develop a concave shape, especially on the long sides of the container. This phenomenon is known as saddling, and it adversely affects the ability of a closure to form a good seal with the upper surface of the finish portion. The saddling is visible in the finite element analysis display that is provided in FIG. 6.
A need exists for an improved blow molded rectangular plastic container that exhibits superior resistance to saddling during the molding process.